The Cal-look Lounge

I got a question for the experienced carb guys.
I think I have an air leak in one of my carbs.
When I put my hand on one airhorn the good one will drop in RPMS and starts to stumble.
But when I put my hand on the airhorn of the other carb, it will go up in RPMS and makes a high note sissing sound.
So no stumble.
Does anybody maybe also had this problem, or know what the problem can be.

Did clean the carbs and put new gaskets in, switched them from side to side than the problem moves also from side to side,
So it is in one carb only.

Thanks in advance.

Eddie

not sure if it wil resolve the issue, but maybe a plugged idle jet?

Hey Eddie,
Just so I am correctly following along, are you using your hand to fully cover the velocity stack or partially cover it?

Lets assume you are partially covering the velocity stack, you are restricting the air causing that cylinder to ritchen up.

If the cylinder starts to drop off as it is now pulling too much fuel, that is a good sign. That cylinder was likely running well.

If the cylinder starts to run normally and the engine picks up that means the cylinder was running lean.

Is the cylinder in question responding normally with the mixture screw? I would check for an intake manifold leak, bad o-ring at the mixture screw, bad o-ring at the idle jet and verify the idle circuit is clean.

Hope these tips help,
Jeremy

I have cleaned them out several times..
It runs ok at idle that is not the problem.

This is what i exactly did, only thing is on one carb the engine stumbles when i clode the trumpet, which is good, but the other one makes a sucking inoise and it starts to climb in rpms instead of stumbling.

Did change the o rings on all screws.

Looks like a leak internal in the carb.
But can not find it.

It runs pretty ok on idle. so that is not the problem.
but as i spray a bit of break cleaner at the carb it goes up in rpms, which indicates a leak.

regards Eddie

Worn throttle shafts allowing air leak.

For me, the most common leak is at the intake manifold to head. I have even ruled out as the problem only to find that it was the problem later. I have not had any luck detecting a leak here by spraying carb cleaner at the gasket.

Tape a piece of sand paper (400-600 grit) to a piece of glass, spray the paper with WD40 or similar and sand down the intake manifold, both seating surfaces until you have verified they are straight.

I also have better luck installing the manifolds first then the carbs to the manifolds. It is easier to feel if they can rock each way from flat as you are cinching them down.

Use new paper gaskets and with the intake manifold on the bench upside down, use a small ball peen hammer around the gasket where it meets the intake manifold port and lightly hammer around the port until the gasket gets scored, lightly cut really.  Put grease on both sides of the gasket to delay them from getting brittle and for easier disassembly later.

This crossed my mind also, but difficult to locate when the carb is in place.
don t feel any play, when of the engine.

Thanks Eddie

Did all that, switch them also rom side to side. Butt they don t seem to be the problem.
Used sealer at the last time i bolt them on.

Regards Eddie

Well you may have to do a smoke test then to see where the leak is coming from.

It most likely sucks air through a non plugged cold start enrichment circuit.

Yep that is what I am thinking at the moment, it makes the same noise as when you apply the cold start function. when you block of the airhorn. (High sissing sound).
How can I fix this problem Torben. Do you have an idea.

Regards Eddie

Ahh good clue. My experience is only with the universal racing style DRLAs that don't have the cold start enrichment system. Are you using the cold start system?

Hy,

I do not use the cold start system, removed it and placed a cover plate over it.
Do I have to do something else to make it work?

Regards Eddie

Eddie I will defer to Torben on the if you should disable the cold start system.

I do know that they sometimes give people trouble on the IDFs and it is common practice to plug the hole on the bottom, see the third post below. With IDFs one or both plungers can lift and begin to leak gas down the manifold. I don't know the failure potential for the DRLA system and if they can leak air as I have only had the universal type.


https://www.thesamba.com/vw/forum/viewtopic.php?t=641914

Ok it wasn t running well anyway, so drilled out the plug and blocked the enrichment circuit.
Bit daring, but have to see if this works, will start her up today.

Fingers crossed.

Thanks for tjis info.

Regards Eddie

ohh this is exciting! Patiently waiting for what you find.
 

Ok did the above, blocked the enrichment circuit with plugs.
Changed the throttle shaft bearings. They felt tight when replacing.
But the engine still kept running strange.
It would not hold steady Rpm s. When the throttle is applied when it goes up to 2500 rpm s if flies to 3500 rpm s, I could not hold it steady for 3000 rpm s it bounces back and forth.
And still when spraying brake fluid on de base of the carb/top of inlet manifold the rpm s go up.
Working on this for months now, getting very frustrated, because I can not find the cause of the problem.

Pulled the 45 dellorto s off, replaced them with my 40mm webers with inlets from my old engine.
Started it, it runs with  out problems.
The engine never sounded so good.  Very sharp throttle response.    
Well I keep it like this for now. But still very curious what the problem with the 45 dellorto s IS.
The 40 are a bit small for the 2.5 liter engine, but put in 34 vebturis and bigger main /air jets.
For now it runs quite ok till 4000 rpm s, did not push it further until I recieve my A/F ratio meter.

Still open for what could be the problem, because I don t know it anymore.

Regards Eddie

What about the fuel pressure They are much more sensitive than the Weber Around 0.17 bar is good

Micke,

I have the fuel pressure at 0.2 bar (with fuel pressure regulator and gauge).

So you made two changes at once, the carbs and the intake manifolds. Since it sounded like you might have an intake manifold leak, why not try putting the 45s back on with the new manifolds and see what that does.

Did all the changes one by one, did about 20 try s. changing one thing at a time.

But you are correct the next one will be the 45 s on the 40 s manifold and look if they willl work.

Thanks